1. Field of the Invention
This invention relates to a hubcap and more particularly to a hubcap for use with automatic bearing lubrication systems and even more particularly to a hubcap having a shielded vent.
2. Description of the Related Art
Hubcaps are used on wheels of many trucks and trailers to prevent contaminants from entering the wheel bearings and for maintaining the oil or grease in the bearings. In recent years, Dual Dynamics, Inc. of Lincoln, Neb. has designed a hubcap having an automatic bearing lubrication system. The hubcap of Dual Dynamics, Inc. is known as a Dual-Guard.TM. hubcap and includes a hubcap which may be mounted on the studs of the truck or trailer wheel or threaded onto some types of axles. The interior of the Dual-Guard.TM. hubcap is filled with oil or grease so that the wheel bearings are lubricated. Heretofore, it has been necessary to provide a small vent opening in the Dual-Guard.TM. hubcap to permit the venting of excessive pressure within the hubcap as the bearings become heated. Although the vent openings work extremely well, they do pose a problem in certain situations. For example, in some dock loading situations, the wheels of the truck move downwardly into an excavated area adjacent the dock so that the bed of the truck will be level with the dock. In some cases, the excavated area adjacent the dock may be filled with water. Should the hubcaps of the truck wheels be submerged in the water, water and other contaminants may enter the interior of the hubcap through the vent opening. The water and contaminants may dramatically shorten the life of the wheel bearings, hub and axle of the truck.
The problems associated with the prior art were solved by way of the disclosure in U.S. Pat. No. 5,192,117 wherein a hubcap is described which includes a vent opening having a plug positioned therein which is comprised of a bronze powder material cast into a cylindrical shape and press-fitted into the vent opening to permit the continuous passage of air therethrough to vent the wheel to vent the wheel bearings, but which prevented the passage of water and other contaminants therethrough. Although the bronze powder material used in the vent of the '117 patent is the preferred embodiment, it has been found that other materials having certain characteristics will also serve the intended purpose. Although the bronze material of plug 36 in U.S. Pat. No. 5,192,117 did perform its intended function, it was found that other materials will work, providing the plug 36 is manufactured from a porous material in which the material, particle size, porosity, pore size, pore shape, tortuosity and interconnection of the pores is such that the plug will readily allow the passage of gasses, but will not allow the passage of fine debris and liquid such as water.
Even though the vents disclosed hereinabove could satisfactorily perform, it has been found that the grease or oil in the bearings tends to come into contact with the inner end of the vent plug and may restrict the flow of air or gasses therethrough.
It is therefore a principal object of the invention to provide an improved hubcap having a shielded vent provided therein.
A further object of the invention is to provide a hubcap having a vented opening formed therein which is filled with a cylindrical plug which permits air to pass therethrough to vent the hubcap, but which prevents water and other contaminants from passing therethrough, with the plug having a shield positioned at its inner end to prevent grease from coming into contact therewith.
These and other objects will be apparent to those skilled in the art.